1. Field of the Invention
This invention relates generally to a roller hearth furnace for heating sheets of glass as the glass is conveyed horizontally through the furnace, and particularly toward such a furnace which is used in a glass tempering system to heat the glass prior to being conveyed through a quench unit where a tempering quench is performed to give the glass desirable mechanical properties.
2. Description of the Prior Art
Glass sheets can be tempered by first heating the sheets and then suddenly cooling them to thereby change the mechanical properties of the glass. The tempering operation increases the strength of the glass and also causes the glass to break into small pieces that are dull and relatively harmless, instead of into large, sharp pieces. To perform the tempering of glass sheets, roller hearth furnaces have been developed in the past to heat the glass sheets prior to their cooling which is usually performed by pressurized air that is sprayed onto the glass. Prior art roller hearth furnaces utilize roller conveyors for conveying the glass sheets through the furnace with their planes oriented horizontally. One such prior art furnace is disclosed by the patent of McMaster et al, U.S. Pat. No. 3,806,312, issued Apr. 23, 1974, and others are shown by the references cited therein. The heated glass is conveyed through a quench unit where the sudden cooling is performed, and cooling units are then used to further cool the glass to a temperature where it can be handled.